JPH07122297A - Non-aqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To improve reserving characteristic and cycle characteristic of a battery using LiPF6 as a material of an electrolyte solute by adding acid anhydride into a non-aqueous electrolyte having hexafluoro lithium phosphate as a solute. CONSTITUTION:A positive electrode 1 and a negative electrode 2 are housed inside a negative electrode jar 7 in a spirally wound state via a separator 3, into which a non-aqueous electrolyte is injected. The positive electrode 1 is connected to a positive electrode outside terminal via a positive electrode lead 4 while the negative electrode 2 is connected to the negative electrode jar 7 via a negative electrode lead 5 so that chemical energy generated inside the battery can be taken out as electric energy. The non-aqueous electrolyte includes mainly hexafluoro lithium phosphate, added with acid anhydride. Consequently, water content contained in a battery system reacts with the acid anhydride, and decomposition of LiPF6 due to the reaction with the water can be restrained when the water content is dissipated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery, and more specifically, to improve storage characteristics (primary and secondary batteries) and cycle characteristics (secondary battery) of the non-aqueous electrolyte battery. , Improvement of non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years,
A non-aqueous electrolyte battery using an alloy or a carbon material capable of inserting and extracting metallic lithium or lithium ions as a negative electrode material has been attracting attention as a battery capable of increasing the capacity.

Lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ) and the like are well known as solutes of the non-aqueous electrolyte used in this type of battery. Above all, L
Since iPF ₆ has a high electric conductivity in the non-aqueous electrolyte solution using it as a solute, and makes it possible to obtain a non-aqueous electrolyte battery exhibiting excellent high rate discharge characteristics, iPF ₆ is one of the most noticeable solutes. Is one.

However, a non-aqueous electrolyte battery using LiPF ₆ is stored for a long period of time, and in the case of a secondary battery, it is in a state after charging (a state in which lithium ions are occluded in the carbon material, or a metal material). If stored for a long period of time in a state where active lithium ions are deposited on the surface of lithium), the water present in the battery system (water in the positive and negative electrodes and water in the electrolyte) or water entering from outside the battery system Li
PF ₆ is decomposed, and the decomposition product reacts with lithium existing in the negative electrode to attach the reaction product to the surface of the negative electrode. As a result, the reaction area of the negative electrode becomes small, and the negative electrode capacity gradually decreases. Therefore, the conventional non-aqueous electrolyte battery has a problem that the storage characteristics are not good regardless of whether it is a primary battery or a secondary battery.

Particularly, in a secondary battery which is repeatedly charged and discharged, the reaction area of the negative electrode gradually decreases as the charging and discharging cycle progresses, so that there is a problem that the cycle characteristics are not good.

The present invention has been made in view of the above circumstances, and an object of the present invention is to preserve characteristics of a non-aqueous electrolyte battery using LiPF ₆ as an electrolyte solute (primary and secondary batteries). And improving cycle characteristics (secondary battery).

[0007]

A non-aqueous electrolyte battery according to the present invention (hereinafter referred to as "the battery of the present invention") according to the present invention for achieving the above object is a positive electrode and stores and releases metallic lithium or lithium ions. In a non-aqueous electrolyte battery comprising a negative electrode having a substance capable of being a negative electrode material and a non-aqueous electrolyte solution having lithium hexafluorophosphate as a solute, it is possible to add an acid anhydride to the non-aqueous electrolyte solution. Characterize.

Typical acid anhydrides are monobasic acids such as acetic anhydride and propionic anhydride and their derivatives, and dibasic acids such as succinic anhydride, phthalic anhydride and maleic anhydride and their derivatives. The acid anhydride may be a liquid (eg, acetic anhydride) or a solid (eg, succinic anhydride).

The amount of the acid anhydride to be added needs to be varied depending on the amount of water contained in the battery, but it is generally 0.1 to 10% by weight based on the total amount of the non-aqueous electrolyte. Is preferred. If it is less than 0.1% by weight, the effect of addition is not sufficiently exhibited, while if it exceeds 10% by weight, the electrolyte solution becomes deficient.

In the present invention, LiPF ₆ is produced by reacting with an acid anhydride to which water is added in the battery system to eliminate it.
It is possible to suppress decomposition of LiPF ₆ due to reaction with water, which has been a problem when solute is used as a solute of the non-aqueous electrolyte, and thereby improve the storage characteristics and cycle characteristics of the non-aqueous electrolyte battery. . Therefore, as the positive electrode material, the negative electrode material, the solvent of the non-aqueous electrolyte solution, and the like, various materials conventionally proposed or put into practical use for the non-aqueous electrolyte battery can be used without particular limitation.

In the case of a secondary battery, positive electrode materials (active materials) include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and L.
iFeO ₂ is exemplified, and MnO ₂ and fluorinated graphite are exemplified as the positive electrode material in the case of the primary battery.

[0012] Examples of the negative electrode material in the case of the secondary battery include metallic lithium and alloys and carbon materials capable of inserting and extracting lithium ions, and examples of the negative electrode material in the case of the primary battery include metallic lithium.

Examples of the solvent include organic solvents such as ethylene carbonate, vinylene carbonate and propylene carbonate, and low solvents such as dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane and ethoxymethoxyethane. A mixed solvent with a boiling point solvent is exemplified.

[0014]

In the present invention, since the acid anhydride is added to the non-aqueous electrolyte, the water generated in the battery system reacts with this acid anhydride to return to the carboxylic acid (for example, acetic anhydride In some cases it reacts with water to form acetic acid). Therefore, LiP when the non-aqueous electrolyte primary battery is stored for a long period of time or the non-aqueous electrolyte secondary battery is stored for a long period of time after being charged.
The decomposition and degradation of F ₆ is suppressed. Therefore, the decomposition product of LiPF ₆ reacts with lithium existing on the negative electrode, and the reduction of the reaction area of the negative electrode due to the reaction product adhering to the surface of the negative electrode is suppressed.

Particularly, in the non-aqueous electrolyte secondary battery, decomposition and deterioration of LiPF ₆ at the time of charging / discharging is also suppressed, so that the decrease in battery capacity with the progress of charging / discharging cycle is suppressed.

[0016]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible.

Example 1 AA type (AA size) non-aqueous electrolyte secondary battery (the battery of the present invention) was produced.

[Positive electrode] LiCoO ₂ as a positive electrode active material produced by heat treatment at 800 ° C., artificial graphite as a conductive agent, and polyvinylidene fluoride as a binder have a weight ratio of 85: 10: 5. As such, a mixture obtained by mixing LiCoO ₂ and artificial graphite is dispersed in a 5 wt% N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride to prepare a slurry, and this slurry is subjected to a doctor blade method. And then applied on both sides of an aluminum foil as a positive electrode current collector, and vacuum dried at 130 ° C. for 2 hours to produce a positive electrode.

[Negative Electrode] The graphite powder was dispersed in a 5 wt% NMP solution of polyvinylidene fluoride so that the weight ratio of the graphite powder and polyvinylidene fluoride was 85:15 to prepare a slurry. After coating on both sides of the copper foil as the negative electrode current collector by the blade method, 100
A negative electrode was produced by vacuum drying at 150 ° C for 2 hours.

[Non-aqueous electrolyte] ethylene carbonate (E
C) and 1,2-dimethoxyethane (DME) in an equal volume mixed solvent, LiPF ₆ is dissolved at a ratio of 1 M (mol / liter), and then acetic anhydride is added and mixed to contain 0.01 M acetic anhydride. A non-aqueous electrolyte was prepared.

[Production of Battery] AA-type battery BA1 of the present invention was produced using the above-described positive and negative electrodes and the non-aqueous electrolyte. As the separator, a polypropylene microporous film (Hoechst Celanese Co., Ltd., trade name “Celgard”) was used and impregnated with the above non-aqueous electrolyte.

FIG. 1 is a cross-sectional view schematically showing the produced battery BA1 of the present invention. The illustrated battery BA1 of the present invention includes a positive electrode 1, a negative electrode 2, a separator 3 for separating the two electrodes, a positive electrode lead 4, and a negative electrode. Lead 5, positive electrode external terminal 6, negative electrode can 7
And so on. The positive electrode 1 and the negative electrode 2 are housed in the negative electrode can 7 in a state of being spirally wound via the separator 3 in which the nonaqueous electrolytic solution is injected, and the positive electrode 1 is externally connected to the positive electrode via the positive electrode lead 4. The terminal 6 and the negative electrode 2 are connected to the negative electrode can 7 via the negative electrode lead 5 so that chemical energy generated inside the battery can be taken out as electric energy to the outside.

Comparative Example 1 A non-aqueous electrolytic solution was prepared in the same manner as in Example 1 except that acetic anhydride was not added. Next, an AA type comparative battery BC1 was produced in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used.

[Cycle Characteristics] With respect to the battery BA1 of the present invention and the comparative battery BC1, the end-of-charge voltage at 200 mA was 4.
After charging to 1V, discharge end voltage is 2.7 at 200mA.
A charging / discharging cycle test in which the step of discharging up to 5 V was defined as one cycle was performed. The results are shown in Figure 2. In this test, the time when the discharge capacity reached 400 mAh was considered to be the battery life, and the test was terminated at that time.

FIG. 2 is a graph showing the cycle characteristics of each battery, in which the vertical axis represents the discharge capacity (mAh) and the horizontal axis represents the number of cycles (times). As shown in FIG. The battery BA1 has a long battery life of about 600 cycles, while the comparative battery BC1 has a short battery life of about 500 cycles. From this fact, LiPF ₆ during charge / discharge cycle
It can be seen that the decrease in the discharge capacity due to the decomposition of the is significantly suppressed by adding acetic anhydride.

FIG. 3 shows the weight ratio (%) of acetic anhydride in the non-aqueous electrolyte and the cycle life (up to a discharge capacity of 400 mAh) when the proportion of acetic anhydride added to the non-aqueous electrolyte was variously changed. Is a graph showing the relationship between the number of cycles (number of times) and the acetic anhydride in the nonaqueous electrolytic solution within the range of 0.1 to 10% by weight. It turns out to be preferable.

[Storage Characteristics] With respect to the battery BA1 of the present invention and the comparative battery BC1, the end-of-charge voltage of 4.1 V at 200 mA.
After being charged up to 60 ° C., it was stored for 10 days (corresponding to storage for about half a year at room temperature), and the battery capacity before and after storage was examined. The results are shown in Table 1.

[0028]

[Table 1]

As is clear from Table 1, the battery BA of the present invention
1 has a very high capacity retention rate of 99%, whereas Comparative Battery BC1 has a low capacity retention rate of 88%. From this, LiPF when stored in the charged state
It can be seen that the decrease in discharge capacity due to the decomposition of ₆ is significantly suppressed by adding acetic anhydride to the non-aqueous electrolyte.

(Example 2) In the same manner as in Example 1 except that an equal volume mixed solvent of propylene carbonate and DME was used in place of the equal volume mixed solvent of EC and DME.
A non-aqueous electrolyte was prepared. Next, an AA-type battery BA2 of the present invention was produced in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used.

Example 3 A nonaqueous electrolytic solution was prepared in the same manner as in Example 2 except that 0.01M of propionic anhydride was added and mixed instead of acetic anhydride. Next, an AA-type battery BA3 of the present invention was produced in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used.

Example 4 A nonaqueous electrolytic solution was prepared in the same manner as in Example 2 except that 0.01M of succinic anhydride was added and mixed instead of acetic anhydride. Next, an AA-type battery BA4 of the present invention was produced in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used.

Comparative Example 2 A non-aqueous electrolyte solution was prepared in the same manner as in Example 2 except that acetic anhydride was not added and mixed. Next, an AA type comparative battery BC2 was produced in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used.

[Cycle Characteristics] Batteries BA2 to BA of the present invention
4 and the comparative battery BC2 were subjected to a charge / discharge cycle test under the same conditions as the above charge / discharge cycle test conditions to examine the cycle characteristics of each battery. The results are shown in Fig. 4. As in the previous charge / discharge cycle test, the discharge capacity was 400 mAh.
The battery life was considered to be the time when the test became, and the test was terminated at that time.

FIG. 4 is a graph showing the cycle characteristics of each battery, in which the vertical axis represents the discharge capacity (mAh) and the horizontal axis represents the number of cycles (times). As shown in FIG. The batteries BA2 to BA4 have a long battery life of 600 cycles or more, while the comparative battery BC2 has a battery life of about 50.
As short as 0 cycles. It is considered that this is also due to the same reason as described in the above [Cycle characteristics].

In the above embodiments, the case where the present invention is applied to the non-aqueous electrolyte secondary battery has been described as an example, but the same excellent effect can be obtained when applied to the non-aqueous electrolyte primary battery. Is obtained.

Further, in the above embodiments, the case where acetic anhydride, propionic anhydride, and succinic anhydride are used as the acid anhydride has been described as an example. However, derivatives such as acetic anhydride, phthalic anhydride, maleic anhydride and Besides these derivatives,
Even when other acid anhydride is used, it is possible to obtain a non-aqueous electrolyte battery exhibiting the same excellent storage characteristics and cycle characteristics.

[0038]

The decomposition and deterioration of LiPF ₆ due to the water content in the battery system is suppressed by the acid anhydride added to the non-aqueous electrolyte solution. Therefore, the battery of the present invention has excellent storage characteristics and is particularly suitable for secondary batteries. As a result, decomposition and deterioration of LiPF ₆ during charging / discharging are less likely to occur, so that cycle characteristics are also excellent.

[Brief description of drawings]

FIG. 1 is a sectional view of an AA battery of the present invention.

FIG. 2 is a graph showing each cycle characteristic of the battery of the present invention and the comparative battery.

FIG. 3 is a graph showing the relationship between the weight ratio (%) of acetic anhydride in the non-aqueous electrolyte and the cycle life (times).

FIG. 4 is a graph showing each cycle characteristic of the battery of the present invention and the comparative battery.

[Explanation of symbols]

 BA1 Inventive battery 1 Positive electrode 2 Negative electrode 3 Separator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Saito 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode having a negative electrode material made of a substance capable of occluding and releasing metallic lithium or lithium ions, and a non-aqueous electrolytic solution having lithium hexafluorophosphate as a solute. A non-aqueous electrolyte battery in which an acid anhydride is added to the non-aqueous electrolyte. 2. The non-aqueous electrolyte battery according to claim 1, wherein the acid anhydride is acetic anhydride, propionic anhydride, succinic anhydride, phthalic anhydride, maleic anhydride or a derivative thereof.